Field of the Invention and Description of the Related Art
This invention relates to a method of inspecting objects by an image pickup means according to which measurements, discoloration tests, etc. can be conducted on certain parts of an object, a picture of which is given by computer-graphics-based drawing means.
An example of an apparatus for measuring the dimensions of certain parts of an object by means of an electronic scope is disclosed in Japanese Laid-Open Patent No. 59-70903, which is shown in FIG. 1.
This prior-art apparatus employs an electronic scope 81 in which illuminating light from a light source apparatus 82 is transmitted through a light guide 83 and emitted through the end surface of a front-end section 84, thereby illuminating an object 85.
A laser-beam transmitting light guide 86 is inserted into this electronic scope 81. This laser-beam transmitting light guide 86 serves to transmit a laser beam from a laser oscillating apparatus 87 and causes it to be emitted through lenses 88, 88 provided at two branch end sections thereof. Two parallel laser beams are emitted through these branch end sections, spaced from each other by a distance d, where impinge upon the object 85, forming two laser spots 89, 89 spaced from each other by the distance d.
An optical image of the illuminated object 85 is formed on a solid image pickup element 92 by an objective lens 91 provided in the front-end section 84, the solid image pickup element 92 being arranged in the focal plane of the objective lens 91. This optical image undergoes photoelectric transfer and is supplied to a video signal processing apparatus 94 through a signal line 93. A standard video signal is generated by this video signal processing apparatus 94 and is displayed on a monitor 95. Suppose the length 1 of a part 96 to be inspected of the object 85 (e.g., a flaw on the object) is to be measured. The actual length 1 can be known from the length of the corresponding image 96' on the display and from the ratio of the actual distance d between the laser spots 89, 89 on the object to the distance between the corresponding spots 89', 89' on the display.
In the above-described conventional apparatus, measurement of length cannot be performed without using the electronic scope 81, which is equipped with the dedicated lenses 88, 88 and light guide 86 for applying the laser beam.
Because of its complicated structure, the electronic scope 81 inevitably includes a front-end section 84 with a large cross section. As a result, the front-end section 84 cannot be inserted into relatively narrow holes.
Besides, with this conventional apparatus, measurement can be conducted only where the object part to be inspected has a planar configuration which is substantially identical to the part where the laser beams are applied.
Apart from this, U.S. Pat. No. 4,725,883 discloses an optical inspection system according to which any damage, etc. to the surface of a tubular product can be detected by means of a feeler. The feeler of this system has to be engaged in a position in the vicinity of the part to be inspected, resulting in the use of this system being restricted to the inspection of the surfaces of tubular products.
A typical use of the industrial electronic scope may be the inspection of turbine blades, etc. in boilers, aircraft engines or the like. In the case of turbine blades or the like, a large number of objects having the same configuration have to be inspected. Further, since they are industrial products, their configuration and dimensions are clarified by drawings, etc.
Now, the development of minicomputers has recently made remarkable progress, making it possible to form solid bodies through computer graphics using inexpensive desk top computers.
With computer graphics, the illuminating light can be applied from an arbitrary angle to an object whose configuration and dimensions are defined, making it possible to visualize on the monitor screen how the object looks from that arbitrary angle.
When observing an object by means of an electronic scope, the distance between the scope and the object varies, so that it is not possible to measure various parts of the object from a displayed picture thereof unless a special electronic scope as described above is employed.
In the case of computer graphics, all the portions of an object, including minute ones, are perfectly controlled by a coordinate system notwithstanding the fact that the object is displayed as it looks to the eye. Accordingly, the actual length of any line segment added to a displayed computer-graphics image can be obtained by calculation. Further, the actual configuration or area of any figure added thereto can also be calculated.
In spite of this advantage, computer graphics have not been applied much to electronic scopes. Thus, no attempt has been made to measure length, etc. by means of computer graphics.
It should be further added that it is difficult to discover a flaw on an object by means of conventional methods if the object has a complicated configuration.